There is a large amount of non-ferrous scrap generated each year and much of it comes from scrapped automobiles. Each year in North America there are approximately 10 million cars and small trucks scrapped by shredding. The cars or trucks are fed into shredders which are a type of large hammer mill, and the shredders smash a complete automobile into small pieces in seconds. After going through the shredder, a large proportion of the non-metallics, such as plastics, foam, carpeting, etc., is removed by air classification. Then steel, which is the main product of the shredder, is removed by magnetic means. This leaves some non-metals (which were not previously removed by the air classification) and some valuable non-ferrous metals such as aluminum, zinc, copper, brass, lead, plated zinc and brass, stainless steel, and perhaps some other non-ferrous metals.
The shredder product of non-ferrous metals is valuable but it is not easy to separate into its various components. One automobile may have of the order of 50 lb. of non-ferrous metal, depending on the make, model and year, and also depending on losses due to prior stripping. Remembering that about 10 million cars and small trucks are scrapped each year in North America, there would be about half a billion pounds of scrap non-ferrous metal produced each year. This material may have a value, at the present time, of about 15 cents per lb. when in an unseparated form, but perhaps about 30 cents per lb. when separated. Thus there is an available increase in value that could be attributed to satisfactory separation of the components of non-ferrous metal scrap of the order of $75 million per year.
In the past this non-ferrous metal scrap has been shipped from the shredders to processing plants which perform the separation. Some of these processing plants are abroad where labour is relatively cheap and the sorting is done by hand. However the majority of non-ferrous metal scrap is separated by a few processing plants which use a sequence of standard metallurgical separating techniques. For example, a first operation might be a heavy media operation which separates non-metals based on specific gravity. A typical media for this separation might be a magnetite material. A subsequent second operation might also be a heavy media operation using a ferrosilicon medium to separate aluminum. A third operation might involve a sweat furnace which separates zinc by a differential melting process. A fourth operation might be a separation by hand of copper bearing metals.
These separation processes remove only one component at a time and the processes must be sequential. It is difficult to accelerate or combine any of these separating processes. In addition, the equipment required is costly, and it is difficult to scale them down, so they cannot conveniently and economically be set up at each shredder. Rather, the scrap from each shredder is sent to a few central processing plants. However it would be desirable, from the standpoint of the shredder operator, to be able to separate the non-ferrous metal scrap at the shredder, and not only enhance the price but avoid the expense of shipping to a central processing plant.
There is another disadvantage connected with a sweat furnace which is used to melt zinc away from copper, brass, stainless steel, etc.. While copper, brass and stainless steel have much higher melting points, lead in the form of solder, balance weights and body filler has a melting point of the same order as zinc. Thus, lead is one of the main contaminents in the grade of zinc and a high lead content can greatly reduce the value of a zinc product.
Because of the desirability of being able to sort non-ferrous metal scrap without using complex metallurgical separation and also be able to do the sorting at the shredder, attempts have been made to sort non-ferrous scrap electronically. Canadian Pat. No. 1,110,996--CLARK et al, issued Oct. 20, 1981, describes a single-line feed type sorter for sorting non-ferrous auto scrap into multiple components. This sorter uses a circular rotating carousel onto which scrap pieces are deposited from a single line feed of scrap on a conveyor. The scrap pieces are moved by the carousel past a light unit which provides a signal representing the size of a piece of scrap, and then beneath a source of high energy radiation and an x-ray fluorescence detector which provides a signal indication of the kind of non-ferrous metal. The carousel floor which supports the scrap pieces comprises a plurality of radially extending keys. There are a plurality of chutes in sequential arrangement beneath the carousel. As a piece of scrap is carried by the carousel past a discharge chute for the particular kind of scrap, the respective keys are released to drop the piece of scrap down the proper chute.
Thus, the separation of the pieces is mechanical, which tends to limit the speed of sorting. Also, the feed is a single-line feed which also limits the speed. Because of the diameter of the carousel, it would be difficult to place several in a parallel arrangement for multiple single-line feed, and it would be difficult to have several conveyors, fed from a single bin, supply multiple carousels in parallel.
Another attempt was made in the late 1970's to adapt a random stream ore sorter to the sorting of non-ferrous auto scrap. A random stream re sorter is described in Canadian Pat. No. 923,601--KELLY et al, issued Mar. 27, 1973. Various illumination/detector combinations were tried including a colour TV camera for a single separation of copper bearing material from the rest of the non-ferrous scrap material. However, a reliable distinction could not be made between copper and pale yellow brass or between some varieties of red primer paint and copper oxide. Thus, while a random stream sorter has a desirably high sorting rate, the apparatus was not able to make a reliable separation of even a single component.